The Julian calendar, proposed by
Julius CaesarJulius Caesar in 46 BC (708
AUC), was a reform of the Roman calendar.[1] It took effect on 1
JanuaryJanuary 45 BC (AUC 709), by edict. It was the predominant
calendar in the Roman world, most of Europe, and in European
settlements in the Americas and elsewhere, until it was refined and
gradually replaced by the Gregorian calendar, promulgated in 1582 by
Pope Gregory XIII. The
Julian calendarJulian calendar gains against the mean tropical
year at the rate of one day in 128 years. For the Gregorian calendar,
the figure is one day in 3,030 years.[2] The difference in the average
length of the year between Julian (365.25 days) and Gregorian
(365.2425 days) is 0.002%.
The
Julian calendarJulian calendar has a regular year of 365 days divided into 12
months, as listed in the table below. A leap day is added to February
every four years. The Julian year is, therefore, on average 365.25
days long. It was intended to approximate the tropical (solar) year.
Although Greek astronomers had known, at least since Hipparchus, a
century before the Julian reform, that the tropical year was slightly
shorter than 365.25 days, the calendar did not compensate for this
difference. As a result, the calendar year gains about three days
every four centuries compared to observed equinox times and the
seasons. This discrepancy was corrected by the Gregorian reform of
1582. The
Gregorian calendarGregorian calendar has the same months and month lengths as
the Julian calendar, but, in the Gregorian calendar, years evenly
divisible by 100 are not leap years, except that years evenly
divisible by 400 remain leap years.[3] Consequently—since 16
FebruaryFebruary Julian/1
MarchMarch 1900 Gregorian and until 15
FebruaryFebruary Julian/28
FebruaryFebruary 2100 Gregorian—the
Julian calendarJulian calendar is currently 13 days
behind the Gregorian calendar.
The
Julian calendarJulian calendar has been replaced as the civil calendar by the
Gregorian calendarGregorian calendar in almost all countries which formerly used it,
although it continued to be the civil calendar of some countries into
the 20th century.[4] Egypt converted on 20
DecemberDecember 1874/1 January
1875.
TurkeyTurkey switched (for fiscal purposes) on 16 February/1 March
1917.
RussiaRussia changed on 1/14
FebruaryFebruary 1918.[5] Greece made the change
for civil purposes on 16 February/1
MarchMarch 1923, but the national day
(25 March), which was a religious holiday, was to remain on the old
calendar. Most Christian denominations in the west and areas
evangelised by western churches have also replaced the Julian calendar
with the Gregorian as the basis for their liturgical calendars.
However, most branches of the Eastern
Orthodox ChurchOrthodox Church still use the
Julian calendarJulian calendar for calculating the date of Easter, upon which the
timing of all the other moveable feasts depends. Some Orthodox
churches have adopted the
Revised Julian calendarRevised Julian calendar for the observance
of fixed feasts, while other Orthodox churches retain the Julian
calendar for all purposes.[6] The
Julian calendarJulian calendar is still used by the
BerbersBerbers of the Maghreb in the form of the Berber calendar,[7] and on
Mount Athos. In the form of the Alexandrian calendar, it is the basis
for the Ethiopian calendar, which is the civil calendar of Ethiopia.
During the changeover between calendars and for some time afterwards,
dual dating was used in documents and gave the date according to both
systems. In contemporary as well as modern texts that describe events
during the period of change, it is customary to clarify to which
calendar a given date refers by using an O.S. or N.S. suffix (denoting
Old Style, Julian or New Style, Gregorian).

Motivation
The ordinary year in the previous
Roman calendarRoman calendar consisted of 12
months, for a total of 355 days. In addition, a 27- or 28-day
intercalary month, the Mensis Intercalaris, was sometimes inserted
between
FebruaryFebruary and March. This intercalary month was formed by
inserting 22 or 23 days after the first 23 days of February; the last
five days of February, which counted down toward the start of March,
became the last five days of Intercalaris. The net effect was to add
22 or 23 days to the year, forming an intercalary year of 377 or 378
days.[10] Some say the mensis intercalaris always had 27 days and
began on either the first or the second day after the Terminalia (23
February).[11]
According to the later writers
Censorinus and Macrobius, the ideal
intercalary cycle consisted of ordinary years of 355 days alternating
with intercalary years, alternately 377 and 378 days long. In this
system, the average Roman year would have had ​366 1⁄4 days
over four years, giving it an average drift of one day per year
relative to any solstice or equinox.
MacrobiusMacrobius describes a further
refinement whereby, in one 8-year period within a 24-year cycle, there
were only three intercalary years, each of 377 days (thus 11
intercalary years out of 24). This refinement averages the length of
the year to 365.25 days over 24 years.
In practice, intercalations did not occur systematically according to
any of these ideal systems, but were determined by the pontifices. So
far as can be determined from the historical evidence, they were much
less regular than these ideal schemes suggest. They usually occurred
every second or third year, but were sometimes omitted for much
longer, and occasionally occurred in two consecutive years.
If managed correctly this system could have allowed the Roman year to
stay roughly aligned to a tropical year. However, since the pontifices
were often politicians, and because a Roman magistrate's term of
office corresponded with a calendar year, this power was prone to
abuse: a pontifex could lengthen a year in which he or one of his
political allies was in office, or refuse to lengthen one in which his
opponents were in power.[12]
If too many intercalations were omitted, as happened after the Second
Punic War and during the Civil Wars, the calendar would drift out of
alignment with the tropical year. Moreover, because intercalations
were often determined quite late, the average Roman citizen often did
not know the date, particularly if he were some distance from the
city. For these reasons, the last years of the pre-Julian calendar
were later known as "years of confusion". The problems became
particularly acute during the years of Julius Caesar's pontificate
before the reform, 63–46 BC, when there were only five
intercalary months (instead of eight), none of which were during the
five Roman years before 46 BC.
Caesar's reform was intended to solve this problem permanently, by
creating a calendar that remained aligned to the sun without any human
intervention. This proved useful very soon after the new calendar came
into effect.
VarroVarro used it in 37 BC to fix calendar dates for the
start of the four seasons, which would have been impossible only 8
years earlier.[13] A century later, when Pliny dated the winter
solstice to 25
DecemberDecember because the sun entered the 8th degree of
Capricorn on that date,[14] this stability had become an ordinary fact
of life.
Context of the reform
Although the approximation of ​365 1⁄4 days for the tropical
year had been known for a long time[15] ancient solar calendars had
used less precise periods, resulting in gradual misalignment of the
calendar with the seasons.
The octaeteris, a cycle of 8 lunar years popularised by Cleostratus
(and also commonly attributed to Eudoxus) which was used in some early
Greek calendars, notably in Athens, is 1.53 days longer than eight
Julian years. The length of nineteen years in the cycle of Meton was
6,940 days, six hours longer than the mean Julian year. The mean
Julian year was the basis of the 76-year cycle devised by
Callippus (a
student under Eudoxus) to improve the Metonic cycle.
In Persia (Iran) after the reform in the Persian calendar by
introduction of the Persian Zoroastrian (i. e. Young Avestan) calendar
in 503 BC and afterwards, the first day of the year (1
Farvardin=Nowruz) slipped against the vernal equinox at the rate of
approximately one day every four years.[16][17]
Likewise in the Egyptian calendar, a fixed year of 365 days was in
use, drifting by one day against the sun in four years. An
unsuccessful attempt to add an extra day every fourth year was made in
238 BC (Decree of Canopus). Caesar probably experienced this
"wandering" or "vague" calendar in that country. He landed in the Nile
delta in
OctoberOctober 48 BC and soon became embroiled in the Ptolemaic
dynastic war, especially after Cleopatra managed to be "introduced" to
him in Alexandria.
Caesar imposed a peace, and a banquet was held to celebrate the
event.[18]
LucanLucan depicted Caesar talking to a wise man called Acoreus
during the feast, stating his intention to create a calendar more
perfect than that of Eudoxus[18] (Eudoxus was popularly credited with
having determined the length of the year to be ​365 1⁄4
days).[19] But the war soon resumed and Caesar was attacked by the
Egyptian army for several months until he achieved victory. He then
enjoyed a long cruise on the Nile with Cleopatra before leaving the
country in
JuneJune 47 BC.[20]
Caesar returned to
RomeRome in 46 BC and, according to Plutarch,
called in the best philosophers and mathematicians of his time to
solve the problem of the calendar.[21] Pliny says that Caesar was
aided in his reform by the astronomer Sosigenes of Alexandria[22] who
is generally considered the principal designer of the reform.
Sosigenes may also have been the author of the astronomical almanac
published by Caesar to facilitate the reform.[23] Eventually, it was
decided to establish a calendar that would be a combination between
the old Roman months, the fixed length of the Egyptian calendar, and
the ​365 1⁄4 days of the Greek astronomy. According to
Macrobius, Caesar was assisted in this by a certain Marcus
Flavius.[24]
Julian reform
Realignment of the year
The first step of the reform was to realign the start of the calendar
year (1 January) to the tropical year by making 46 BC (708 AUC)
445 days long, compensating for the intercalations which had been
missed during Caesar's pontificate. This year had already been
extended from 355 to 378 days by the insertion of a regular
intercalary month in February. When Caesar decreed the reform,
probably shortly after his return from the African campaign in late
QuintilisQuintilis (July), he added 67 more days by inserting two extraordinary
intercalary months between
NovemberNovember and December.[25]
These months are called Intercalaris Prior and Intercalaris Posterior
in letters of
CiceroCicero written at the time; there is no basis for the
statement sometimes seen that they were called "Undecimber" and
"Duodecimber", terms that arose in the 18th century over a millennium
after the Roman Empire's collapse.[26] Their individual lengths are
unknown, as is the position of the Nones and Ides within them.[27]
Because 46 BC was the last of a series of irregular years, this
extra-long year was, and is, referred to as the "last year of
confusion". The new calendar began operation after the realignment had
been completed, in 45 BC.[28]
Changes to the months
The Julian months were formed by adding ten days to a regular
pre-Julian Roman year of 355 days, creating a regular Julian year of
365 days. Two extra days were added to January,
SextilisSextilis (August) and
December, and one extra day was added to April, June,
SeptemberSeptember and
November.
FebruaryFebruary was not changed in ordinary years, and so continued
to be the traditional 28 days. Thus, the ordinary (i.e., non-leap
year) lengths of all of the months were set by the
Julian calendarJulian calendar to
the same values they still hold today. (See Sacrobosco's theory on
month lengths below for stories purporting otherwise.)
The Julian reform did not change the method used to account days of
the month in the pre-Julian calendar, based on the Kalends, Nones and
Ides, nor did it change the positions of these three dates within the
months.
MacrobiusMacrobius states that the extra days were added immediately
before the last day of each month to avoid disturbing the position of
the established religious ceremonies relative to the Nones and Ides of
the month.[29] However, since Roman dates after the Ides of the month
counted down toward the start of the next month, the extra days had
the effect of raising the initial value of the count of the day
following the Ides in the lengthened months. Thus, in January,
SextilisSextilis and
DecemberDecember the 14th day of the month became a.d. XIX Kal.
instead of a.d. XVII Kal., while in April, June,
SeptemberSeptember and
NovemberNovember it became a.d. XVIII Kal.
Romans of the time born after the Ides of a month responded
differently to the effect of this change on their birthdays. Mark
Antony kept his birthday on 14 January, which changed its date from
a.d. XVII Kal. Feb to a.d. XIX Kal. Feb, a date that had previously
not existed.
LiviaLivia kept the date of her birthday unchanged at a.d. III
Kal. Feb., which moved it from 28 to 30 January, a day that had
previously not existed.
AugustusAugustus kept his on 23 September, but both
the old date (a.d. VIII Kal. Oct.) and the new (a.d. IX Kal. Oct.)
were celebrated in some places.
The inserted days were all initially characterised as dies fasti (F
– see Roman calendar).[30] The character of a few festival days was
changed. In the early Julio-
ClaudianClaudian period a large number of
festivals were decreed to celebrate events of dynastic importance,
which caused the character of the associated dates to be changed to
NP. However, this practice was discontinued around the reign of
Claudius, and the practice of characterising days fell into disuse
around the end of the first century AD: the Antonine jurist Gaius
speaks of dies nefasti as a thing of the past.[31]
Intercalation
The old intercalary month was abolished. The new leap day was dated as
ante diem bis sextum Kalendas Martias ('the sixth doubled before the
Kalends of March'), usually abbreviated as a.d. bis VI Kal. Mart.;
hence it is called in English the bissextile day. The year in which it
occurred was termed annus bissextus, in English the bissextile year.
There is debate about the exact position of the bissextile day in the
early Julian calendar. The earliest direct evidence is a statement of
the 2nd century jurist Celsus, who states that there were two halves
of a 48-hour day, and that the intercalated day was the "posterior"
half. An inscription from AD 168 states that a.d. V Kal. Mart. was the
day after the bissextile day. The 19th century chronologist Ideler
argued that Celsus used the term "posterior" in a technical fashion to
refer to the earlier of the two days, which requires the inscription
to refer to the whole 48-hour day as the bissextile. Some later
historians share this view. Others, following Mommsen, take the view
that Celsus was using the ordinary
LatinLatin (and English) meaning of
"posterior". A third view is that neither half of the 48-hour "bis
sextum" was originally formally designated as intercalated, but that
the need to do so arose as the concept of a 48-hour day became
obsolete.[32]
There is no doubt that the bissextile day eventually became the
earlier of the two days for most purposes. In 238
Censorinus stated
that it was inserted after the Terminalia (23 February) and was
followed by the last five days of February, i.e., a.d. VI, V, IV, III
and prid. Kal. Mart. (which would be 24 to 28
FebruaryFebruary in a common
year and the 25th to 29th in a leap year). Hence he regarded the
bissextum as the first half of the doubled day. All later writers,
including
MacrobiusMacrobius about 430,
BedeBede in 725, and other medieval
computists (calculators of Easter) followed this rule, as does the
liturgical calendar of the Roman Catholic Church. However, Celsus'
definition continued to be used for legal purposes. It was
incorporated into Justinian's Digest,[33] and in the English statute
De anno et die bissextili of 1236,[34] which was not formally repealed
until 1879.
The effect of the bissextile day on the nundinal cycle is not
discussed in the sources. According to Dio Cassius, a leap day was
inserted in 41 BC to ensure that the first market day of
40 BC did not fall on 1 January, which implies that the old 8-day
cycle was not immediately affected by the Julian reform. However, he
also reports that in AD 44, and on some previous occasions, the market
day was changed to avoid a conflict with a religious festival. This
may indicate that a single nundinal letter was assigned to both halves
of the 48-hour bissextile day by this time, so that the
Regifugium and
the market day might fall on the same date but on different days. In
any case, the 8-day nundinal cycle began to be displaced by the 7-day
week in the first century AD, and dominical letters began to appear
alongside nundinal letters in the fasti.[35]
During the late
Middle AgesMiddle Ages days in the month came to be numbered in
consecutive day order. Consequently, the leap day was considered to be
the last day in
FebruaryFebruary in leap years, i.e., 29 February, which is
its current position.
Sacrobosco's theory on month lengths
The Julian reform set the lengths of the months to their modern
values. However, a 13th-century scholar, Sacrobosco, proposed a
different explanation for the lengths of Julian months[36] which is
still widely repeated but is certainly wrong.
According to Sacrobosco, the month lengths for ordinary years in the
Roman Republican calendar, from
JanuaryJanuary to December, were:

30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29.

SacroboscoSacrobosco then thought that
Julius CaesarJulius Caesar added one day to every
month except February, a total of 11 more days to regular months,
giving the ordinary Julian year of 365 days. A single leap day could
now be added to this extra short February:

31, 29/30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30.

He then said
AugustusAugustus changed this, by taking one day from
FebruaryFebruary to
add it to Sextilis, and then modifying the alternation of the
following months, to:

31, 28/29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31

so that the length of
AugustusAugustus (August) would not be shorter than (and
therefore inferior to) the length of Iulius (July), giving us the
irregular month lengths which are still in use.
There is abundant evidence disproving this theory. First, a wall
painting of a
Roman calendarRoman calendar predating the Julian reform has
survived,[37] which confirms the literary accounts that the months
were already irregular before
Julius CaesarJulius Caesar reformed them, with an
ordinary year of 355 days, not 354, with month lengths arranged as:

29, 28, 31, 29, 31, 29, 31, 29, 29, 31, 29, 29.

Also, the Julian reform did not change the dates of the Nones and
Ides. In particular, the Ides were late (on the 15th rather than 13th)
in March, May,
JulyJuly and October, showing that these months always had
31 days in the Roman calendar,[38] whereas Sacrobosco's theory
requires that March,
MayMay and
JulyJuly were originally 30 days long and
that the length of
OctoberOctober was changed from 29 to 30 days by Caesar
and to 31 days by Augustus. Further, Sacrobosco's theory is explicitly
contradicted by the 3rd and 5th century authors Censorinus[39] and
Macrobius,[40] and it is inconsistent with seasonal lengths given by
Varro, writing in 37 BC,[13] before
SextilisSextilis was renamed for
AugustusAugustus in 8 BC, with the 31-day
SextilisSextilis given by an Egyptian
papyrus from 24 BC,[41] and with the 28-day
FebruaryFebruary shown in the
FastiFasti Caeretani, which is dated before 12 BC.[42]
Adoption of the Julian calendar

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Caesar's reform only applied to the Roman calendar. However, in the
following decades many of the local civic and provincial calendars of
the empire and neighbouring client kingdoms were aligned to the Julian
calendar by transforming them into calendars with years of 365 days
with an extra day intercalated every four years.[43] The reformed
calendars typically retained many features of the unreformed
calendars. In many cases, the New
YearYear was not on 1 January, the leap
day was not on the bissextile day, the old month names were retained,
the lengths of the reformed months did not match the lengths of Julian
months, and, even if they did, their first days did not match the
first day of the corresponding Julian month. Nevertheless, since the
reformed calendars had fixed relationships to each other and to the
Julian calendar, the process of converting dates between them became
quite straightforward, through the use of conversion tables known as
hemerologia.[44] Several of the reformed calendars are only known
through surviving hemerologia.
The three most important of these calendars are the Alexandrian
calendar, the Asian calendar and the Syro-Macedonian calendar. Other
reformed calendars are known from Cappadocia, Cyprus and the cities of
Syria and Palestine. Most reformed calendars were adopted under
Augustus, though the calendar of
NabateaNabatea was reformed after the
kingdom became the
Roman provinceRoman province of Arabia in AD 106. There is no
evidence that local calendars were aligned to the
Julian calendarJulian calendar in
the western empire. Unreformed calendars continued to be used in Gaul,
Greece, Macedon, the Balkans and parts of Palestine, most notably in
Judea.
The
Alexandrian calendarAlexandrian calendar adapted the
Egyptian calendarEgyptian calendar by adding a 6th
epagomenal day as the last day of the year in every fourth year,
falling on 29
AugustAugust preceding a Julian bissextile day. It was
otherwise identical to the Egyptian calendar. The first leap day was
in 22 BC, and they occurred every four years from the beginning,
even though Roman leap days occurred every three years at this time
(see
Leap yearLeap year error). This calendar influenced the structure of
several other reformed calendars, such as those of the cities of Gaza
and Ascalon in Palestine, Salamis in Cyprus, and the province of
Arabia. It was adopted by the Coptic church and remains in use both as
the liturgical calendar of the Coptic church and as the civil calendar
of Ethiopia.
The Asian calendar was an adaptation of the Macedonian calendar used
in the province of Asia and, with minor variations, in nearby cities
and provinces. It is known in detail through the survival of decrees
promulgating it issued in 8 BC by the proconsul Paullus Fabius
Maximus. It renamed the first month Dios as Kaisar, and arranged the
months such that each month started on the ninth day before the
kalends of the corresponding Roman month; thus the year began on 23
September, Augustus' birthday. Since Greek months typically had 29 or
30 days, the extra day of 31-day months was named Sebaste—the
emperor's day—and was the first day of these months. The leap day
was a second Sebaste day in the month of Xandikos, i.e., 24 February.
This calendar remained in use at least until the middle of the fifth
century AD.
The Syro-Macedonian calendar was an adaptation of the Macedonian
calendar used in
AntiochAntioch and other parts of Syria. The months were
exactly aligned to the Julian calendar, but they retained their
Macedonian names and the year began in Dios =
NovemberNovember until the fifth
century, when the start of the year was moved to Gorpiaios =
September.
These reformed calendars generally remained in use until the fifth or
sixth century. Around that time most of them were replaced as civil
calendars by the Julian calendar, but with a year starting in
SeptemberSeptember to reflect the year of the indiction cycle.
The
Julian calendarJulian calendar spread beyond the borders of the Roman Empire
through its use as the Christian liturgical calendar. When a people or
a country was converted to Christianity, they generally also adopted
the Christian calendar of the church responsible for conversion. Thus,
Christian Nubia and
EthiopiaEthiopia adopted the Alexandrian calendar, while
Christian Europe adopted the Julian calendar, in either the Catholic
or Orthodox variant. Starting in the 16th century, European
settlements in the Americas and elsewhere likewise inherited the
Julian calendarJulian calendar of the mother country, until they adopted the
Gregorian reform. The last country to adopt the
Julian calendarJulian calendar was
the Ottoman Empire, which used it for financial purposes for some time
under the name
Rumi calendarRumi calendar and dropped the "escape years" which tied
it to Muslim chronology in 1840.
Leap yearLeap year error
Although the new calendar was much simpler than the pre-Julian
calendar, the pontifices initially added a leap day every three years,
instead of every four. There are accounts of this in Solinus,[45]
Pliny,[46] Ammianus,[47] Suetonius,[48] and Censorinus.[49]
Macrobius[50] gives the following account of the introduction of the
Julian calendar:
"Caesar’s regulation of the civil year to accord with his revised
measurement was proclaimed publicly by edict, and the arrangement
might have continued to stand had not the correction itself of the
calendar led the priests to introduce a new error of their own; for
they proceeded to insert the intercalary day, which represented the
four quarter-days, at the beginning of each fourth year instead of at
its end, although the intercalation ought to have been made at the end
of each fourth year and before the beginning of the fifth.
"This error continued for thirty-six years by which time twelve
intercalary days had been inserted instead of the number actually due,
namely nine. But when this error was at length recognised, it too was
corrected, by an order of Augustus, that twelve years should be
allowed to pass without an intercalary day, since the sequence of
twelve such years would account for the three days which, in the
course of thirty-six years, had been introduced by the premature
actions of the priests."
So, according to Macrobius,

the year was considered to begin after the Terminalia, (23
February)[51]
the calendar was operated correctly from its introduction on 1 January
45 BC until the beginning of the fourth year (February
42 BC) at which point the priests inserted the first
intercalation,
Caesar's intention was to make the first intercalation at the
beginning of the fifth year (
FebruaryFebruary 41 BC),
the priests made a further eleven intercalations after 42 BC at
three-year intervals so that the twelfth intercalation fell in
9 BC,
had Caesar's intention been followed there would have been
intercalations every four years after 41 BC, so that the ninth
intercalation would have been in 9 BC,
after 9 BC, there were twelve years without leap years, so that
the leap days Caesar would have had in 5 BC, 1 BC and
AD 4 were omitted and
after AD 4 the calendar was operated as Caesar intended, so that
the next leap year was AD 8 and then leap years followed every
fourth year thereafter.[52]

Some people have had different ideas as to how the leap years went.
The above scheme is that of Scaliger in the table below. He
established that the Augustan reform was instituted in 8 BC. The
table shows for each reconstruction the implied proleptic Julian date
for the first day of Caesar's reformed calendar (Kal. Ian. AUC 709)
and the first Julian date on which the
Roman calendarRoman calendar date matches the
Julian calendarJulian calendar after the completion of Augustus' reform.
Alexander Jones claims that the correct
Julian calendarJulian calendar was in use in
Egypt in 24 BC,[41] implying that the first day of the reform in
both Egypt and Rome, 1
JanuaryJanuary 45 BC, was the Julian date
1
JanuaryJanuary if 45 BC was a leap year and 2
JanuaryJanuary if it
was not. This necessitates fourteen leap days up to and including
AD 8 if 45 BC was a leap year and thirteen if it was not.
Pierre Brind'Amour[53] argued that "only one day was intercalated
between 1/1/45 and 1/1/40 (disregarding a momentary 'fiddling' in
DecemberDecember of 41[54] to avoid the nundinum falling on Kal. Ian."[55]

Scholar
Date
Triennial leap years (BC)
First Julian day
First aligned day
Quadriennial leap year resumes

In 1999, a papyrus was discovered which gives the dates of
astronomical phenomena in 24 BC in both the Egyptian and Roman
calendars. From 30
AugustAugust 26 BC (Julian), Egypt had two calendars: the
old Egyptian in which every year had 365 days and the new Alexandrian
in which every fourth year had 366 days. Up to 28
AugustAugust 22 BC
(Julian) the date in both calendars was the same. The dates in the
Alexandrian and Julian calendars are in one-to-one correspondence
except for the period from 29
AugustAugust in the year preceding a Julian
leap year to the following 24 February.[64] From a comparison of the
astronomical data with the Egyptian and Roman dates, Alexander
Jones[41] concluded that the Egyptian astronomers (as opposed to
travellers from Rome) used the correct Julian calendar.
An inscription has been discovered[65] which orders a new calendar to
be used in Asia to replace the previous Greek lunar calendar.
According to one translation[66]
"Intercalation shall commence on the day after 14 Peritius [a.d. IX
Kal. Feb, which would have been 15 Peritius] as it is currently
constituted in the third year following promulgation of the decree.
Xanthicus shall have 32 days in this intercalary year."
This is historically correct. It was decreed by the proconsul that the
first day of the year in the new calendar shall be Augustus' birthday,
a.d. IX Kal. Oct. Every month begins on the ninth day before the
kalends. The date of introduction, the day after 14 Peritius, was 1
Dystrus, the next month. The month after that was Xanthicus. Thus
Xanthicus began on a.d. IX Kal. Mart., and normally contained 31 days.
In leap year, however, it contained an extra "Sebaste day", the Roman
leap day, and thus had 32 days. From the lunar nature of the old
calendar we can fix the starting date of the new one as
24 January, a.d. IX Kal. Feb 5 BC in the Julian calendar, which
was a leap year. Thus from inception the dates of the reformed Asian
calendar are in one-to-one correspondence with the Julian.
Another translation of this inscription[67] is
"Intercalation shall commence on the day after the fourteenth day in
the current month of Peritius [a.d. IX Kal. Feb], occurring every
third year. Xanthicus shall have 32 days in this intercalary year."
This would move the starting date back three years to 8 BC, and
from the lunar synchronism back to 26
JanuaryJanuary (Julian). But since the
corresponding Roman date in the inscription is 24 January, this must
be according to the incorrect calendar which in 8 BC
AugustusAugustus had
ordered to be corrected by the omission of leap days. As the authors
of the previous paper point out, with the correct four-year cycle
being used in Egypt and the three-year cycle abolished in
RomeRome it is
unlikely that
AugustusAugustus would have ordered the three-year cycle to be
introduced in Asia.
MonthMonth names
The Julian reform did not immediately cause the names of any months to
be changed. The old intercalary month was abolished and replaced with
a single intercalary day at the same point (i.e., five days before the
end of February).
JanuaryJanuary continued to be the first month of the year.
The Romans later renamed months after
Julius CaesarJulius Caesar and Augustus,
renaming
QuintilisQuintilis as "Iulius" (July)[8] in 44 BC and
SextilisSextilis as
"Augustus" (August) in 8 BC.
QuintilisQuintilis was renamed to honour
Caesar because it was the month of his birth.[68] According to a
senatus consultum quoted by Macrobius,
SextilisSextilis was renamed to honour
AugustusAugustus because several of the most significant events in his rise to
power, culminating in the fall of Alexandria, occurred in that
month.[69]
Other months were renamed by other emperors, but apparently none of
the later changes survived their deaths. In AD 37,
CaligulaCaligula renamed
SeptemberSeptember as "Germanicus" after his father;[70] in AD 65,
NeroNero renamed
AprilApril as "Neroneus",
MayMay as "Claudius" and
JuneJune as "Germanicus";[71]
and in AD 84
DomitianDomitian renamed
SeptemberSeptember as "Germanicus" and
OctoberOctober as
"Domitianus".[72]
CommodusCommodus was unique in renaming all twelve months
after his own adopted names (
JanuaryJanuary to December): "Amazonius",
"Invictus", "Felix", "Pius", "Lucius", "Aelius", "Aurelius",
"Commodus", "Augustus", "Herculeus", "Romanus", and
"Exsuperatorius".[73] The emperor
TacitusTacitus is said to have ordered that
September, the month of his birth and accession, be renamed after him,
but the story is doubtful since he did not become emperor before
NovemberNovember 275.[74] Similar honorific month names were implemented in
many of the provincial calendars that were aligned to the Julian
calendar.[75]
Other name changes were proposed but were never implemented. Tiberius
rejected a senatorial proposal to rename
SeptemberSeptember as "Tiberius" and
OctoberOctober as "Livius", after his mother Livia.[76] Antoninus Pius
rejected a senatorial decree renaming
SeptemberSeptember as "Antoninus" and
NovemberNovember as "Faustina", after his empress.[77]
Much more lasting than the ephemeral month names of the post-Augustan
Roman emperors were the Old High German names introduced by
Charlemagne. According to his biographer,
CharlemagneCharlemagne renamed all of
the months agriculturally into German.[78] These names were used until
the 15th century, over 700 years after his rule, and continued, with
some modifications, to see some use as "traditional" month names until
the late 18th century. The names (
JanuaryJanuary to December) were:
Wintarmanoth ("winter month"), Hornung,[79] Lentzinmanoth ("spring
month", "
LentLent month"), Ostarmanoth ("
EasterEaster month"), Wonnemanoth
("joy-month", a corruption of Winnimanoth "pasture-month"),
Brachmanoth ("fallow-month"), Heuuimanoth ("hay month"), Aranmanoth
("reaping month"), Witumanoth ("wood month"), Windumemanoth ("vintage
month"), Herbistmanoth ("harvest month"), and Heilagmanoth ("holy
month").
The calendar month names used in western and northern Europe, in
Byzantium, and by the Berbers, were derived from the
LatinLatin names.
However, in eastern Europe older seasonal month names continued to be
used into the 19th century, and in some cases are still in use, in
many languages, including: Belarusian, Bulgarian, Croatian, Czech,
Finnish,[80] Georgian, Lithuanian, Macedonian, Polish, Romanian,
Slovene, Ukrainian. When the
Ottoman EmpireOttoman Empire adopted the Julian
calendar, in the form of the Rumi calendar, the month names reflected
Ottoman tradition.
YearYear numbering
The principal method used by the Romans to identify a year for dating
purposes was to name it after the two consuls who took office in it,
the eponymous period in question being the consular year. Beginning in
153 BC, consuls began to take office on 1 January, thus
synchronizing the commencement of the consular and calendar years. The
calendar year has begun in
JanuaryJanuary and ended in
DecemberDecember since about
450 BC according to
OvidOvid or since about 713 BC according to
MacrobiusMacrobius and
PlutarchPlutarch (see Roman calendar).
Julius CaesarJulius Caesar did not
change the beginning of either the consular year or the calendar year.
In addition to consular years, the Romans sometimes used the regnal
year of the emperor, and by the late 4th century documents were also
being dated according to the 15-year cycle of the indiction. In 537,
Justinian required that henceforth the date must include the name of
the emperor and his regnal year, in addition to the indiction and the
consul, while also allowing the use of local eras.
In 309 and 310, and from time to time thereafter, no consuls were
appointed.[81] When this happened, the consular date was given a count
of years since the last consul (so-called "post-consular" dating).
After 541, only the reigning emperor held the consulate, typically for
only one year in his reign, and so post-consular dating became the
norm. Similar post-consular dates were also known in the west in the
early 6th century. The system of consular dating, long obsolete, was
formally abolished in the law code of Leo VI, issued in 888.
Only rarely did the Romans number the year from the founding of the
city (of Rome), ab urbe condita (AUC). This method was used by Roman
historians to determine the number of years from one event to another,
not to date a year. Different historians had several different dates
for the founding. The
FastiFasti Capitolini, an inscription containing an
official list of the consuls which was published by Augustus, used an
epoch of 752 BC. The epoch used by Varro, 753 BC, has been
adopted by modern historians. Indeed,
RenaissanceRenaissance editors often added
it to the manuscripts that they published, giving the false impression
that the Romans numbered their years. Most modern historians tacitly
assume that it began on the day the consuls took office, and ancient
documents such as the
FastiFasti Capitolini which use other AUC systems do
so in the same way. However, Censorinus, writing in the 3rd century
AD, states that, in his time, the AUC year began with the Parilia,
celebrated on 21 April, which was regarded as the actual anniversary
of the foundation of Rome.[82]
Many local eras, such as the
Era of Actium and the Spanish Era, were
adopted for the
Julian calendarJulian calendar or its local equivalent in the
provinces and cities of the Roman Empire. Some of these were used for
a considerable time.[83] Perhaps the best known is the
Era of Martyrs,
sometimes also called Anno Diocletiani (after Diocletian), which was
associated with the
Alexandrian calendarAlexandrian calendar and often used by the
Alexandrian Christians to number their Easters during the 4th and 5th
centuries, and continues to be used by the Coptic and Ethiopian
churches.
In the eastern Mediterranean, the efforts of Christian chronographers
such as Annianus of
AlexandriaAlexandria to date the Biblical creation of the
world led to the introduction of
Anno MundiAnno Mundi eras based on this
event.[84] The most important of these was the Etos Kosmou, used
throughout the Byzantine world from the 10th century and in Russia
until 1700. In the west, the kingdoms succeeding the empire initially
used indictions and regnal years, alone or in combination. The
chronicler Prosper of Aquitaine, in the fifth century, used an era
dated from the Passion of Christ, but this era was not widely adopted.
Dionysius Exiguus proposed the system of
Anno DominiAnno Domini in 525. This era
gradually spread through the western Christian world, once the system
was adopted by Bede.
The
Julian calendarJulian calendar was also used in some Muslim countries. The Rumi
calendar, the
Julian calendarJulian calendar used in the later years of the Ottoman
Empire, adopted an era derived from the lunar AH year equivalent to AD
1840, i.e., the effective Rumi epoch was AD 585. In recent years, some
users of the
Berber calendarBerber calendar have adopted an era starting in
950 BC, the approximate date that the Libyan pharaoh Sheshonq I
came to power in Egypt.
New Year's Day
The
Roman calendarRoman calendar began the year on 1 January, and this remained the
start of the year after the Julian reform. However, even after local
calendars were aligned to the Julian calendar, they started the new
year on different dates. The
Alexandrian calendarAlexandrian calendar in Egypt started on
29
AugustAugust (30
AugustAugust after an Alexandrian leap year). Several local
provincial calendars were aligned to start on the birthday of
Augustus, 23 September. The indiction caused the Byzantine year, which
used the Julian calendar, to begin on 1 September; this date is still
used in the Eastern
Orthodox ChurchOrthodox Church for the beginning of the
liturgical year. When the
Julian calendarJulian calendar was adopted in AD 988 by
Vladimir I of Kiev, the year was numbered
Anno MundiAnno Mundi 6496, beginning
on 1 March, six months after the start of the Byzantine Anno Mundi
year with the same number. In 1492 (AM 7000), Ivan III, according to
church tradition, realigned the start of the year to 1 September, so
that AM 7000 only lasted for six months in Russia, from 1
MarchMarch to 31
AugustAugust 1492.[85]
During the
Middle AgesMiddle Ages 1
JanuaryJanuary retained the name
New Year's DayNew Year's Day (or
an equivalent name) in all western European countries (affiliated with
the Roman Catholic Church), since the medieval calendar continued to
display the months from
JanuaryJanuary to
DecemberDecember (in twelve columns
containing 28 to 31 days each), just as the Romans had. However, most
of those countries began their numbered year on 25
DecemberDecember (the
Nativity of Jesus), 25
MarchMarch (the Incarnation of Jesus), or even
Easter, as in
FranceFrance (see the
Liturgical yearLiturgical year article for more
details).
In Anglo-Saxon England, the year most commonly began on 25 December,
which, as (approximately) the winter solstice, had marked the start of
the year in pagan times, though 25
MarchMarch (the equinox) is occasionally
documented in the 11th century. Sometimes the start of the year was
reckoned as 24 September, the start of the so-called "western
indiction" introduced by Bede.[86] These practices changed after the
Norman conquest. From 1087 to 1155 the English year began on 1
January, and from 1155 to 1751 began on 25 March.[87] In 1752 it was
moved back to 1 January. (See
CalendarCalendar (New Style) Act 1750).
Even before 1752, 1
JanuaryJanuary was sometimes treated as the start of the
new year – for example by Pepys[88] – while the "year starting
25th
MarchMarch was called the Civil or Legal Year".[89] To reduce
misunderstandings on the date, it was not uncommon for a date between
1
JanuaryJanuary and 24
MarchMarch to be written as "1661/62". This was to explain
to the reader that the year was 1661 counting from
MarchMarch and 1662
counting from
JanuaryJanuary as the start of the year.[90] (For more detail,
see Dual dating).
Most western European countries shifted the first day of their
numbered year to 1
JanuaryJanuary while they were still using the Julian
calendar, before they adopted the Gregorian calendar, many during the
16th century. The following table shows the years in which various
countries adopted 1
JanuaryJanuary as the start of the year. Eastern European
countries, with populations showing allegiance to the Orthodox Church,
began the year on 1
SeptemberSeptember from about 988. The
Rumi calendarRumi calendar used
in the
Ottoman EmpireOttoman Empire began the civil year on 1
MarchMarch until 1918.

From Julian to Gregorian
Main article: Gregorian calendar
The
Julian calendarJulian calendar was in general use in Europe and northern Africa
until 1582, when
Pope Gregory XIIIPope Gregory XIII promulgated the Gregorian calendar.
Reform was required because too many leap days are added with respect
to the astronomical seasons on the Julian scheme. On average, the
astronomical solstices and the equinoxes advance by about 11 minutes
per year against the Julian year. As a result, the calculated date of
EasterEaster gradually moved out of alignment with the
MarchMarch equinox.

This is a visual example of the official date change from the Julian
calendar to the Gregorian.

While
HipparchusHipparchus and presumably Sosigenes were aware of the
discrepancy, although not of its correct value,[98] it was evidently
felt to be of little importance at the time of the Julian reform.
However, it accumulated significantly over time: the Julian calendar
gained a day about every 134 years. By 1582, it was ten days out of
alignment from where it supposedly had been in 325 during the Council
of Nicaea.
The
Gregorian calendarGregorian calendar was soon adopted by most Catholic countries
(e.g., Spain, Portugal, Poland, most of Italy). Protestant countries
followed later, and some countries of eastern Europe even later. In
the
British EmpireBritish Empire (including the American colonies), Wednesday 2
SeptemberSeptember 1752 was followed by Thursday 14
SeptemberSeptember 1752. For 12
years from 1700
SwedenSweden used a modified Julian calendar, and adopted
the
Gregorian calendarGregorian calendar in 1753.
Since the Julian and Gregorian calendars were long used
simultaneously, although in different places, calendar dates in the
transition period are often ambiguous, unless it is specified which
calendar was being used. In some circumstances, double dates might be
used, one in each calendar. The notation "Old Style" (O.S.) is
sometimes used to indicate a date in the Julian calendar, as opposed
to "New Style" (N.S.), which either represents the Julian date with
the start of the year as 1
JanuaryJanuary or a full mapping onto the
Gregorian calendar. This notation is used to clarify dates from
countries which continued to use the
Julian calendarJulian calendar after the
Gregorian reform, such as Great Britain, which did not switch to the
reformed calendar until 1752, or Russia, which did not switch until
1918. This is why the Russian Revolution of 7
NovemberNovember 1917 N.S. is
known as the
OctoberOctober Revolution, because it began on 25
OctoberOctober OS.
Throughout the long transition period, the
Julian calendarJulian calendar has
continued to diverge from the Gregorian. This has happened in
whole-day steps, as leap days which were dropped in certain centennial
years in the
Gregorian calendarGregorian calendar continued to be present in the Julian
calendar. Thus, in the year 1700 the difference increased to 11 days;
in 1800, 12; and in 1900, 13. Since 2000 was a leap year according to
both the Julian and Gregorian calendars, the difference of 13 days did
not change in that year: 29
FebruaryFebruary 2000 (Gregorian) fell on 16
FebruaryFebruary 2000 (Julian). This difference will persist until the last
day of
FebruaryFebruary 2100 (Gregorian), since 2100 is not a Gregorian leap
year, but is a Julian leap year. Monday 1
MarchMarch 2100 (Gregorian) falls
on Monday 16
FebruaryFebruary 2100 (Julian).[99]
Eastern Orthodox usage

Russian iconRussian icon of the Theophany (the baptism of
JesusJesus by John the
Baptist) (6 January), the highest-ranked feast which occurs on the
fixed cycle of the Eastern Orthodox liturgical calendar.

Although most Eastern Orthodox countries (most of them in eastern or
southeastern Europe) had adopted the
Gregorian calendarGregorian calendar by 1924, their
national churches had not. The "Revised Julian calendar" was endorsed
by a synod in
ConstantinopleConstantinople in
MayMay 1923, consisting of a solar part
which was and will be identical to the
Gregorian calendarGregorian calendar until the
year 2800, and a lunar part which calculated
EasterEaster astronomically at
Jerusalem. All Orthodox churches refused to accept the lunar part, so
almost all Orthodox churches continue to celebrate
EasterEaster according to
the
Julian calendarJulian calendar (with the exception of the Estonian Orthodox
Church and the Finnish Orthodox Church).[100][101]
The solar part of the
Revised Julian calendarRevised Julian calendar was accepted by only
some Orthodox churches. Those that did accept it, with hope for
improved dialogue and negotiations with the western denominations,
were the Ecumenical Patriarchate of Constantinople, the Patriarchates
of Alexandria, Antioch, the Orthodox Churches of Greece, Cyprus,
Romania, Poland (from 1924 to 2014; it is still permitted to use the
Revised Julian calendarRevised Julian calendar in parishes that want it), Bulgaria (the last
in 1963), and the
Orthodox ChurchOrthodox Church in America (although some OCA
parishes are permitted to use the Julian calendar). Thus these
churches celebrate the Nativity on the same day that western
Christians do, 25
DecemberDecember Gregorian until 2799.
The Orthodox Churches of Jerusalem, Russia, Serbia, Montenegro, Poland
(from 15
JuneJune 2014), Macedonia, Georgia, Ukraine, and the Greek Old
Calendarists and other groups continue to use the Julian calendar,
thus they celebrate the Nativity on 25
DecemberDecember Julian (which is 7
JanuaryJanuary Gregorian until 2100). The Russian
Orthodox ChurchOrthodox Church has some
parishes in the west which celebrate the Nativity on 25 December
Gregorian until 2799.
Parishes of the
Orthodox ChurchOrthodox Church in America Bulgarian Diocese, both
before and after the 1976 transfer of that diocese from the Russian
Orthodox ChurchOrthodox Church Outside
RussiaRussia to the
Orthodox ChurchOrthodox Church in America, were
permitted to use this date. Some
Old CalendaristOld Calendarist groups which stand in
opposition to the state churches of their homelands will use the Great
Feast of the Theophany (6
JanuaryJanuary Julian/19
JanuaryJanuary Gregorian) as a
day for religious processions and the Great Blessing of Waters, to
publicise their cause.[citation needed]
The
Oriental OrthodoxOriental Orthodox Churches generally use the local calendar of
their homelands. However, when calculating the Nativity Feast, most
observe the Julian calendar. This was traditionally for the sake of
unity throughout Christendom. In the west, some Oriental Orthodox
Churches either use the
Gregorian calendarGregorian calendar or are permitted to observe
the Nativity according to it. The Armenian Apostolic Orthodox Church
celebrates the Nativity as part of the Feast of Theophany according to
its traditional calendar.[citation needed]
See also

^ Richards 2013, p. 595.
^ Using value from Richards (2013, p. 587) for tropical year in mean
solar days, the calculation is 1/(365.2425-365.24217)
^ Introduction to Calendars. (15
MayMay 2013).
United StatesUnited States Naval
Observatory.
^ Social Security Administration publication GN 00307.180 –
Gregorian/Julian calendar.
^ Social Security Administration (26
AugustAugust 2005). "GN 00307.180
Gregorian/Julian calendar". Retrieved 27
JulyJuly 2016. Although the
Russian authorities officially changed calendars in 1918, individual
registrars particularly in remote areas continued to use the old
calendar for as long as ten years.
^ Towards a Common Date of Easter. (5–10 March). World Council of
Churches/Middle East Council of Churches Consultation, Aleppo, Syria.
^ Oxby, Clare (1998). "The manipulation of time: Calendars and power
in the Sahara". Nomadic Peoples, New Series. 2 (1/2): 137–149.
JSTOR 43123542.
^ a b c The letter J was not invented until the 16th century.
^ The spelling Quinctilis is also attested; see page 669 of The Oxford
Companion to the Year.
^ T H Key, "A Dictionary of Greek and Roman Antiquities" (article
Calendarium), London, 1875, available at [1].
^ Blackburn, B & Holford-Strevens, L The Oxford Companion to the
Year, Oxford University Press, 1999, reprinted with corrections, 2003,
pp. 669–70.
^ Censorinus, De die natali 20.7 (Latin)
^ a b Varro, On Agriculture I.1.28.
^ Pliny, Natural History: (Book 18, LIX / LXVI / LXVIII / LXXIV).
^ Parker, R. A. (
MayMay 1974). "Ancient Egyptian Astronomy".
Philosophical Transactions of the Royal Society of London. Series A,
Mathematical and Physical Sciences. 276 (1257): 51–65.
JSTOR 74274.
^ Hartner, Willy. "The young Avestan and Babylonian calendars and the
antecedents of precession." Journal for the
HistoryHistory of
AstronomyAstronomy 10
(1979): 1. pp. 1–22. doi:10.1177/002182867901000102
^ Stern, Sacha. Calendars in antiquity: Empires, states, and
societies. Oxford University Press, 2012., p. 178.
^ a b Lucan, Pharsalia: Book 10.
^ Émile Biémont, Rythmes du temps, astronomie et calendriers, éd.
De Boeck (Bruxelles), 2000 (ISBN 2-8041-3287-0), p. 224.
^ Suetonius, Caesar 52.1.
^ Plutarch, Lives of the Noble Grecians and Romans: Caesar 59.
^ Pliny, Natural History: (Book 18, LVII).
^ Encyclopædia Britannica Sosigenes of Alexandria.
^ Macrobius, Saturnalia I.14.2 (Latin).
^ It is not known why he decided that 67 was the correct number of
days to add, nor whether he intended to align the calendar to a
specific astronomical event such as the winter solstice. Ideler
suggested (Handbuch der mathematischen und technischen Chronologie II
123–125) that he intended to align the winter solstice to a
supposedly traditional date of 25 December. The number may compensate
for three omitted intercalary months (67 = 22+23+22). It also made the
distance from 1
MarchMarch 46 BC, the original New Years
DayDay in the
Roman calendar, to 1
JanuaryJanuary 45 BC 365 days.
^ e.g., "... we have a sidelight on what was involved in "the year of
confusion" as it was called. According to Dion Cassius, the historian,
there was a governor in Gaul who insisted that, in the lengthened
year, two months' extra taxes should be paid. The extra months were
called
Undecimber and Duodecimber." (P. W. Wilson, The romance of the
calendar (New York, 1937), 112). The eponymous dating of the cited
passage (Dio Cassius 54.21) shows that it actually refers to an event
of 15 BC, not 46 BC.
^ J. Rüpke, The Roman
CalendarCalendar from Numa to Constantine: Time,
HistoryHistory and the Fasti, 117f., suggests, based on the ritual structures
of the calendar, that 5 days were added to
NovemberNovember and that the two
intercalary months each had 31 days, with Nones and Ides on the 7th
and 15th.
^ William Smith, Dictionary of Greek and Roman Antiquities:
YearYear of
Julius Caesar), following Ideler, interprets Macrobius, Saturnalia
1.14.13 (Latin) to mean that Caesar decreed that the first day of the
new calendar began with the new moon which fell on the night of 1/2
JanuaryJanuary 45 BC. (The new moon was on 2
JanuaryJanuary 45 BC (in the
Proleptic Julian calendar) at 00:21 UTC, according to IMCCE (a branch
of the Paris Observatory): Phases of the moon (between −4000 and
+2500) Archived 2011-07-20 at the Wayback Machine..) However, more
recent studies of the manuscripts have shown that the word on which
this is based, which was formerly read as lunam, should be read as
linam, meaning that
MacrobiusMacrobius was simply stating that Caesar published
an edict giving the revised calendar – see e.g., p.99 in the
translation of
MacrobiusMacrobius by P. Davies. Smith gives no source or
justification for his other speculation that Caesar originally
intended to commence the year precisely with the winter solstice.
^ Macrobius, Saturnalia 1.14.9 (Latin). Exceptionally, the extra day
in
AprilApril was inserted as the 26th, a.d. VI Kal. Mai. in the Julian
calendar, in order to avoid adding a day to the Floralia, which ran
from a.d. IV Kal. Mai. (27
AprilApril in the pre-Julian calendar) to a.d. V
Non. Mai.
^ Macrobius, Saturnalia 1.14.12 (Latin).
^ A. K. Michels, The
CalendarCalendar of the
Roman RepublicRoman Republic Appendix II; J.
Rüpke, The Roman
CalendarCalendar from Numa to Constantine 113–114,
126–132, 147.
^ W. Sternkopf, "Das Bissextum", (JCP 41 (1895) 718–733).
^ Justinian, Digest 50.16.98.
^ "The statute De anno et die bissextili, made at Westminster, Anno 21
Hen. III. and Anno Dom. 1236". The Statutes at Large from Magna Charta
to the End of the Reign of King Henry the Sixth. 1. London.
1763.
^ Dio Cassius 48.33.4, 60.24.7; C. J. Bennett, "The Imperial Nundinal
Cycle", Zeitschrift für Papyrologie und Epigraphik 147 (2004)
175–179.
^ Roscoe Lamont, "The
Roman calendarRoman calendar and its reformation by Julius
Caesar", Popular
AstronomyAstronomy 27 (1919) 583–595. Sacrobosco's theory is
discussed on pages 585–587.
^ Roman Republican calendar.
^ Macrobius, Saturnalia 1.13.7 and 1.14.7–8 (Latin), Censorinus, De
die natali 20.10 (Latin), (English).
^ Censorinus, De die natali 20.9 (Latin), (English)
^ Macrobius, Saturnalia 1.14.7 (Latin)
^ a b c Alexander Jones, Calendrica II: Date Equations from the Reign
of Augustus, Zeitschrift fűr Papyrologie und Epigraphik 129 (2000)
159–166, available at [2].
^ A. Degrassi, Inscriptiones Italiae XIII:
FastiFasti et Elogia 2: Fasti
Anni Numani et Iuliani; Accedunt Feralia, Menologia Rustica,
Parapegmata (Rome, 1963) 66 (Latin)
^ This section is based on S. Stern, Calendars in Antiquity (OUP 2012)
pp. 259–297.
^ Studied in detail in W. Kubitschek, Die Kalendarbücher von Florenz,
Rom und Leyden (Vienna, 1915).
^ Gaius Julius Solinus, De mirabilibus mundi, c.3, available at [3].
^ Gaius Plinius Secundus, Natural History, Vol. 2, 18.57, tr. J
Bostock and H T Riley, London 1855, available at [4][permanent dead
link].
^ The Roman
HistoryHistory of Ammianus Marcellinus, 26.10, Loeb Classical
Library vol. II, Harvard 1940, available at [5].
^ Gaius
SuetoniusSuetonius Tranquillus, Life of Julius Caesar, 40.1, Loeb
Classical Library, Harvard 1913, available at [6].
^ Censorinus, The Natal Day, 20.30, tr. William Maude, New York 1900
available at [7].
^
MacrobiusMacrobius Ambrosius Theodosius, Saturnalia, 1.14.13–1.14.14, tr.
Percival Vaughan Davies, New York 1969,
LatinLatin text at [8]
^ Marcus Terentius Varro, On the
LatinLatin Language, 6.13, tr. Roland
Kent, London 1938 available at [9].
^ Nautical Almanac Offices of the United Kingdom and the United
States. (1961). Explanatory Supplement to the Astronomical Ephemeris
and the American
EphemerisEphemeris and Nautical Almanac, London: Her Majesty's
Stationery Office. p. 410–11.
^ Pierre Brind'Amour, Le calendrier romain, Ottawa 1983, pp. 45–46.
^ Dio Cassius 48.33.4, tr. Earnest Cary, Loeb Classical Library, 9
vol., Harvard 1914–1927, available at [10].
^ Refutation of Brind'Amour's theory by John Ward, Re: Intercalation
in 45BC to 8AD, East Carolina University
CalendarCalendar discussion List
CALNDR-L,
AprilApril 1998.
^ C. J. Bennett, "The Early Augustan Calendars in
RomeRome and Egypt",
Zeitschrift fűr Papyrologie und Epigraphik 142 (2003) 221–240 and
"The Early Augustan Calendars in
RomeRome and Egypt: Addenda et
Corrigenda", Zeitschrift fűr Papyrologie und Epigraphik 147 (2004)
165–168; see also Chris Bennett, A.U.C. 730 = 24 B.C. (Egyptian
papyrus).
^ W. Soltau, Römische Chronologie (Freiburg, 1889) 170–173. He
accepted Matzat's phase of the triennial cycle but argued that it was
absurd to suppose that Caesar would have made the second Julian year a
leap year and that the 36 years had to be accounted from 45 BC.
^ H. Matzat, Römische Chronologie I (Berlin, 1883), 13–18. His
argument rested on Dio Cassius 48.33.4 which mentions a leap day
inserted in 41 BC, "contrary to the (i.e., Caesar's) rule", in
order to avoid having a market day on the first day of 40 BC. Dio
stated that this leap day was compensated for "later". Matzat proposed
this was done by omitting a scheduled leap day in 40 BC, rather
than by omitting a day from an ordinary year.
^ C. L. Ideler, Handbuch der mathematischen und technischen
Chronologie (Berlin, 1825) II 130–131. He argued that Caesar would
have enforced the bissextile day by introducing it in his first
reformed year. T. E. Mommsen, Die Römische Chronologie bis auf Caesar
(Berlin, 1859) 282–299, provided additional circumstantial
arguments.
^ J. Kepler, De Vero Anno Quo Æternus Dei Filius Humanan Naturam in
Utero Benedictæ Virginis Mariæ Assumpsit (Frankfurt, 1614) Cap. V,
repub. in F. Hammer (ed.), Johannes Keplers Gesammelte Werke (Berlin,
1938) V 28.
^ a b c d For the list of triennial leap years proposed by Bünting,
Christmann and Harriot, see Harriot's comparative table reproduced by
Simon Cassidy (Fig. 6). The table numbers years as Julian years, where
Julian year 1 = 45 BC. Thus, Scaliger and Clavius (col. 7) resume
intercalation in Julian year 53 = AD 8, while Bünting (col. 8) and
Harriot (col. 3) resume it in Julian year 49 = AD 4 and Christmann
(col. 9) in year 52 = AD 7.
^ J. Christmann Muhamedis Alfragani arabis chronologica et astronomica
elementa (Frankfurt, 1590), 173. His argument assumed that the
triennial cycle started in the third Julian year.
^ J. J. Scaliger, De emendatione temporum (Paris, 1583), 159, 238.
^ Dieter Hagedorn, Zum aegyptischen Kalender unter Augustus,
Zeitschrift fűr Papyrologie und Epigraphik 100 (1994) 211–222,
available at [11].
^ OGIS 458 (Greek).
^ B A Buxton and R Hannah in Studies in
LatinLatin Literature and Roman
HistoryHistory (ed. C Deroux), XII 290.
^ U. Laffi, "Le iscrizioni relative all'introduzione nel 9 a.c. del
nuovo calendario della provincia d'Asia", Studi Classici e Orientali
16 (1967) 5–99.
^ Suetonius, Caesar 76.1.
^ Suetonius,
AugustusAugustus 31.2; Macrobius, Saturnalia 1.12.35 (Latin)
^ Suetonius,
CaligulaCaligula 15.2.
^ Tacitus, Annals 15.74, 16.12.
^ Suetonius,
DomitianDomitian 13.3.
^ Dio Cassius 73.15.3.
^ Historia Augusta,
TacitusTacitus 13.6. On the chronology see R. McMahon,
Tacitus.
^ Surveyed in K. Scott, Honorific Months, Yale Classical Studies 2
(1931) 201–278.
^ Suetonius,
TiberiusTiberius 26.2.
^ Historia Augusta,
Antoninus PiusAntoninus Pius 10.1.
^ Einhard, Life of Charlemagne, 29.
^ This name of February, the only name in the list without the "month"
suffix, is explained by König, Festschrift Bergmann (1997), pp. 425
ff. as a collective of horn, taken to refer to the antlers shed by red
deer during this time. Older explanations compare the name with Old
Frisian horning (Anglo-Saxon hornung-sunu, Old Norse hornungr) meaning
"bastard, illegitimate son", taken to imply a meaning of
"disinherited" in reference to
FebruaryFebruary being the shortest of months.
^ "Calendar, Finnish". English-Word Information.
^ Chronography of AD 354.
^
Censorinus De die natali 21.6 (Latin). Because the festivities
associated with the
PariliaParilia conflicted with the solemnity of Lent,
which was observed until the Saturday before
EasterEaster Sunday, the early
Roman church did not celebrate
EasterEaster after 21
AprilApril – Charles W.
Jones, "Development of the
LatinLatin Ecclesiastical calendar", Bedae Opera
de Temporibus (1943), 1–122, p.28.
^ For a partial survey see A. E. Samuel, Greek and Roman Chronology:
calendars and years in classical antiquity (Munich, 1972), 245ff.
Samuel introduces his survey by saying: "The number of eras which came
into use and then expired to be replaced by yet other eras during
Hellenistic and Roman times is probably not infinite, but I have not
been able to find the end of them." Anatolian eras are exhaustively
surveyed in W. Leschhorn, Antike Ären: Zeitrechnung, Politik und
Geschichte im Schwarzmeerraum und in Kleinasien nördlich des Tauros
(Stuttgart, 1993).
^ A. A. Mosshammer, The
EasterEasterComputusComputus and the Origins of the
Christian
Era (Oxford, 2008) 27–29.
^ История календаря в России и в СССР
(
CalendarCalendar history in
RussiaRussia and in the USSR).
^ M. L. R. Beaven, "The Regnal Dates of Alfred, Edward the Elder, and
Athelstan", English Historical Review 32 (1917) 517–531; idem, "The
Beginning of the
YearYear in the Alfredian
Chronicle (866–87)", English
Historical Review 33 (1918) 328–342.
^ Catholic Encyclopedia, General
ChronologyChronology (Beginning of the Year).
^ Pepys Diary, "I sat down to end my journell for this year, ..."
^ Spathaky, Mike
Old Style and New Style datesOld Style and New Style dates and the change to the
Gregorian calendar.
^ Spathaky, Mike
Old Style and New Style datesOld Style and New Style dates and the change to the
Gregorian calendar. "An oblique stroke is by far the most usual
indicator, but sometimes the alternative final figures of the year are
written above and below a horizontal line, as in a fraction (a form
which cannot easily be reproduced here in ASCII text). Very
occasionally a hyphen is used, as 1733-34."
^ John James Bond, "Commencement of the Year", Handy-book of rules and
tables for verifying dates with the Christian era, (London: 1875),
91–101.
^ Mike Spathaky Old Style and New Style Dates and the change to the
Gregorian Calendar: A summary for genealogists.
^ The source has Germany, whose current area during the sixteenth
century was a major part of the Holy Roman Empire, a religiously
divided confederation. The source is unclear as to whether all or only
parts of the country made the change. In general, Roman Catholic
countries made the change a few decades before Protestant countries
did.
^ Sweden's conversion is complicated and took much of the first half
of the 18th century. See Swedish calendar.
^ Per decree of 16
JuneJune 1575. Hermann Grotefend, "Osteranfang" (Easter
beginning), Zeitrechnung de Deutschen Mittelalters und der Neuzeit
(
ChronologyChronology of the German
Middle AgesMiddle Ages and modern times) (1891–1898).
^ 1751 in England only lasted from 25
MarchMarch to 31 December. The dates
1
JanuaryJanuary to 24
MarchMarch which would have concluded 1751 under the old
calendar became part of 1752 when the beginning of the numbered year
was changed from 25
MarchMarch to 1 January.
^ See
Rumi calendarRumi calendar for details. It is often stated that Turkey
adopted the
Gregorian calendarGregorian calendar in 1926 or 1927. This refers to the
adoption of the Anno domini era.
^ Richards 1998, p. 216.
^ Walker 2009.
^ "Estonian
Orthodox ChurchOrthodox Church (Estonian Events)". Vancouveri Eesti
Apostliku Õigeusu Kirik. 2010.
^ Bishop Photius of Triaditsa, "The 70th Anniversary of the
Pan-Orthodox Congress, Part II of II"; "HELSINGIN SANOMAT
(International edition)". 21
SeptemberSeptember 2007.